D346 MARINE ENGINE Generator Lead Connections Caterpillar

Generator Lead Connections
1.1. Lead Numbering
2.1. Neutral Connections
3.2. Single Units
4.2. Multiple Units
5.1. Voltage Connections
6.2. Three Phase
7.2. Single Phase Current From A Three-Phase Generator

Lead Numbering

Each coil lead is marked according to the following diagram.

Numbering is clockwise from the top and from the outside in. Terminal TO is the neutral lead on all high voltage connections. On low voltage connections TO is connected with T4, T5, and T6 to form the neutral terminal. The standard generator diagram and the terminal connections are on the nameplate of each generator.

Neutral Connections

Single Units

Three Wire: In a three phase, three wire system, the generator should normally be grounded according to local wiring codes. In some cases, however, it is undesirable to ground the neutral wire. For example, on boats a grounded neutral may increase the problem of electrolysis. In applications where definite measures are taken to prevent grounds to the load leads, an ungrounded neutral can be used. Be sure to check your local wiring codes.

Four Wire: In a three phase, four wire system, the neutral wire should be grounded according to local wiring codes. For only single unit operation, there should never be a need for a disconnect switch, or device, in the neutral line.

Multiple Units

Operation of multiple generators in parallel, having all neutrals grounded, may result in current circulating through the neutral connections. To eliminate the possibility of circulating currents, ground the neutral of only one generator. If multiple generators are alternated on line, a single pole single throw knife switch should be installed in the neutral ground circuit of each generator, so all but one neutral ground circuit can be opened. Be sure one neutral ground circuit is closed.

Voltage Connections

Three Phase

The connections for both high and low voltage are given in the following diagrams.


The terminals must be connected securely and insulated with a good quality electrical tape.


Single Phase Current From A Three-Phase Generator

Three phase and single phase current can be taken simultaneously from a generator connected for three phase service. Connecting the load to any two of the three phase leads will provide single phase voltage at the same voltage as three phase power. Connecting the load to any phase lead and to neutral will produce voltage at 58% of the three phase voltage. DO NOT exceed the nameplate current rating for any one phase.

Single phase power taken from a three phase source can be a problem unless the single phase loading is equally distributed.